Axial fan with adjustable blades



Jan. 25, 1966 KARL-ERIK FERMER 3,231,313

AXIAL FAN WITH ADJUSTABLE BLADES Filed July 13, 1964 FIG. I.

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United States Patent 3,231,313 AXIAL FAN WITH ADJUSTABLE BLADES Karl-Erik Fermr, Jonkoping, Sweden, assignor to Aktiebolaget Svenska Flaktfabriken, Stockholm, Sweden Filed July 13, 1964, Ser. No. 382,010 Claims priority, application Sweden, July 12, 1963, 7,7 61/ 63 4 Claims. (Cl. 302-.-37)

The present invention relates to improvements in axial fans for the transport of dust laden gases, the fans being equipped with adjustable fan blades. Adjustability is provided by journalled axles mounted in the fan hub, and an axially displaceable adjustment means projecting into the hub and adapted to actuate rotating levers mounted on the blade journals. In the present instance the adjustment means is enclosed in a casing designed as a stationary central body portion mounted on the outlet side of the impeller with a diameter corresponding to the fan hub.

In order to prevent, in fans of the above-described type, jamming of the apparatus by dust accumulating at the base of the blades and in the gaps around the base plates of the blades and axles, so-called scavenging air is supplied to the impeller in such a manner that the air passes out over the blades and keeps these portions clean of dust deposits. Fans of this type are described in the US. patent to Ljungstrom, #3,138,3l0. In most cases, however, this step was proved insuflicient to ensure a safe adjustment of the fan blades by the control power available. The reason for this is that on the outlet side of the fan dust laden gas can enter through the gap between the fan hub and the casing which encloses the adjusting device. As a result, dust can accumulate on parts on said device projecting into the hub and thereby render the operation of said device diflicult if not impossible.

In view of the above it is the principal object of the present invention to eliminate the aforesaid disadvantages. In the illustrated instance the fan comprises a cover disk mounted on the open side of the fan hub and is provided with a central, flanged aperture for the adjusting device. An annular chamber encloses the flange and is provided with seals in abutting engagement against the flange, the chamber being mounted on the frontal wall portion of the casing body which faces the impeller. The chamber is connected to air supply means for the supply of air under pressure (barrier air) for preventing the dust laden gas from entering through the gap between the casing body and the fan hub.

According to one embodiment of the invention the fan may be constructed such that scavenging air also can be supplied in a known manner for cleaning the fan blades and their bearings.

The invention will now be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a fragmentary sectional view of an axial fan constructed in accordance with the invention; and

FIG. 2 is a fragmentary sectional view taken along line 22 of FIG. 1.

Referring now to the drawing, 1 is an axial impeller comprising a radially extending concentric hub 2 mounted on a rotatable shaft 3 and provided with a plurality of adjustable-pitch fan blades 4 rotatably journalled in the hub and disposed about the periphery thereof, and an enclosing cylindrical casing 5. Each of the blades is provided with a circular base plate 6 and an axle 7 mounted in two ball bearings 8 in a recess in the hub. A lever 9 is connected at the inner or other end of the axle facing the center, and in the present instance supports a rotatably mounted roller 10. Adjustment means comprising an axially displaceable adjusting disk 12 having a peripheral groove 11, is adapted to be moved forward and backward "ice by a shaft 13 by a control means (not shown), and by engaging the lever to effect adjustment of the pitch of the blades to the desired angle with the plane of rotation. In the present instance the disk connects to the lever through the roller 10 and the groove 11. The control means of the adjustment means is enclosed in a stationary casing 14 designed as the central body, and is mounted on the outlet side of the impeller with a diameter substantially corresponding to that of the hub.

According to the invention on an inwardly, sloping frontal wall 14a of the casing confronting the impeller, an annular hollow chamber 15 is mounted and connected by a pipe 16 to air supply means, in the present instance a blower 27 for the supply of air under pressure. Inwardly projecting forward and rear walls 17a and 17b respectively of the chamber, have termini adjacent to but spaced from a flange 19 on a conically shaped cover disk 20 mounted on the open side of the hub. The flange 19 defines a central aperture 21 to receive and circumscribe the shaft of the adjusting device. In order to prevent air from leaking axially rearward (to the left as viewed in FIG. 1), a radial seal is connected to at least the rear one of the walls 17 b of the chamber and engages with the cover disk 20 which rotates with the hub 2. In the present instance both walls 17a and 1711 are provided with such seals 18a and 18b respectively, while the for-ward seal 18a may only loosely engage the cover disk. The reason for the loose engagement is that by supplying a relatively small amount of air to the annular chamber 15 an overpressure can be maintained in the chamber 15. By air leaking out through the space 28 between the sealing 18a and the flange 19 an air stream is produced in an annular slot comprising a space 22 and a gap 23. Thus the air stream has an outward direction through the space 22 and the gap 23, the hub and the cover disk 20 along with the frontal wall 14a defining the slot and thereby preventing the dust laden gas transported by the fan from entering through the gap.

For cleaning the blades and their bearings the journals of the blades are provided in a known maner with boreholes 24 and 25 connected to an air supply means (not shown) and an opening the the gap 26 about the base plate of the fan blade.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only 'by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be made without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. In an axial fan for transporting dust laden gases comprising a radially-extending concentric hub mounted on a rotatable shaft, a plurality of adjustable-pitch fan blades disposed about the periphery of said hub, said hub having recesses about its periphery, a circular base plate and a rotatable axle mounting each of said blades intermediate a recess in said hub and said blades, said axle mounting a lever at its inner end, adjustment means comprising an axially disposed adjustable shaft mounting a disk, said disk connected to said lever so as to cause changes of pitch in said blades upon axial displacement of said shaft, an annular cover disk connected to said hub and having a central terminus defining an aperture to receive and circumscribe said adjustable shaft; a stationary casing mounted on the outlet side of said impeller and having a frontal wall portion confronting said hub and said cover disk and spaced therefrom so as to define an annular slot therebetween, an inwardly projecting pair of spaced walls defining a hollow chamber connected to said frontal wall portion and having termini adjacent to but spaced from said cover disk, a radial seal connected to at least the rear one of said Walls and in abutting en- 7 gagement with said cover disk, and air supply means connected to said chamber to provide a flow of air from said chamber into said annular slot between said frontal wall portion and said cover disk whereby dust laden gas is prevented from entering therebetween.

2. In an axial fan for transporting dust laden gases in accordance with claim 1 wherein said cover disk is conical in configuration and wherein said terminus of said cover disk has a flanged portion projecting axially along said adjustable shaft, said frontal wall portion having an inward slope and said casing having an outer diameter substantially equal to the diameter of said hub and a rotatable axle mounting each of said blades intermediate a recess in said hub and said blades, said axle mounting a lever at its inner end, adjustment means comprising an axially disposed adjustable shaft mounting a disk, said disk connected to said lever so as to cause a change of pitch in said blades upon axial displacement of said shaft, an annular cover disk connected to said hub and having a central flanged portion to receive and circumscribe said adjustable shaft; a stationary casing mounted on the outlet side of said impeller having an inwardly sloping frontal wall portion confronting said hub and said cover disk and spaced therefrom so as to define an annular slot therebetween, an inwardly projecting pair of spaced walls defining a hollow chamber connected to said frontal wall portion and having termini adjacent to but spaced from said radial extremity of said flanged portion of said cover disk, a radial seal connected to at least the rear one of said walls and in engagement with said flanged portion, and air supply means connected to said chamber to provide a flow of air from said chamber into said annular slot between said frontal wall portion and said cover disk whereby dust laden gas is prevented from entering therebetween.

4. In an axial fan for transporting dust laden gases in accordance with claim 3 wherein said forward one of said spaced walls has a radial seal connected thereto and in loose engagement with said flanged portion.

References Cited by the Examiner UNITED STATES PATENTS 3,029,011 4/1962 Lewis. 3,101,890 8/1963 Carlson 230-132 3,139,310 6/1964 Ljungstrom 30237 HUGO O. SCHULZ, Primary Examiner.

A. H. NIELSEN, Assistant Examiner. 

1. IN AN AXIAL FAN FOR TRANSPORTING DUST LADEN GASES COMPRISING A RADIALLY-EXTENDING CONCENTRIC HUB MOUNTED ON A ROTATABLE SHAFT, A PLURALITY OF ADJUSTABLE-PITCH FAN BLADES DISPOSED ABOUT THE PERIPHERY OF SAID HUB, SAID HUB HAVING RECESSES ABOUT ITS PERIPHERY, A CIRCULAR BASE PLATE AND A ROTATABLE AXLE MOUNTING EACH OF SAID BLADES INTERMEDIATE A RECESS IN SAID HUB AND SAID BLADES, SAID AXLE MOUNTING A LEVER AT ITS INNER END, ADJUSTMENT MEANS COMPRISING A AXIALLY DISPOSED ADJUSTABLE SHAFT MOUNTING A DISK, SAID DISK CONNECTED TO SAID LEVER SO AS TO CAUSE CHANGES OF PITCH IN SAID BLADES UPON AXIAL DISPLACEMENT OF SAID SHAFT, AN ANNULAR COVER DISK CONNECTED TO SAID HUB AND HAVING A CENTRAL TERMINUS DEFINING AN APERTURE TO RECEIVE A CIRCUMSCRIBE SAID ADJUSTABLE SHAFT; A STATIONARY CASING MOUNTED ON THE OUTLET SIDE OF SAID IMPELLER AND HAVING A FRONTAL WALL PORTION CONFRONTING SAID HUB AND SAID COVER DISK AND SPACED THEREFROM SO AS TO DEFINE AN ANNULAR SLOT BETWEEN, AN INWARDLY PROJECTING PAIR OF SPACED WALLS DEFINING A HOLLOW CHAMBER CONNECTED TO SAID FRONTAL WALL PORTION AND HAVING TERMINI ADJACENT TO BUT SPACED FROM SAID COVER DISK, A RADIAL SEAL CONNECTED TO AT LEAST THE REAR ONE OF SAID WALLS AND IN ABUTTING ENGAGEMENT WITH SAID COVER DISK, AND AIR SUPPLY MEANS CONNECTED TO SAID CHAMBER TO PROVIDE A FLOW OF AIR FROM SAID CHAMBER INTO SAID ANNULAR SLOT BETWEEN SAID FRONTAL WALL PORTION AND SAID COVER DISK WHEREBY DUST LADEN GAS IS PREVENTED FROM ENTERING THEREBETWEEN. 